Case IH 161-11 - DEC – Transmission Control Unit (TCU) / Transmission Control Module (TCM): Transmission Input Shaft Speed Sensor Plausibility Error

The Transmission Control Unit is comparing the speed signal from the input shaft to the engine RPM (crankshaft speed) and finding that the two values do not logically align (e.g., the input shaft speed is reading zero or an erratic value while the engine is running and the clutch is engaged). This mismatch causes erratic shifting, failure to shift, or a complete loss of drive.

• MAGNUM AFS Connect
• Puma
• Puma 200 CVT
• Maxxum
• Magnum
• Steiger

1. 1

   Locate the input shaft speed sensor (accessible externally on the transmission housing) and inspect the wiring harness for open circuits, chafing, or short circuits to the battery/ground.

2. 2

   Disconnect the sensor and inspect the connector pins for corrosion, moisture, or bent terminals.

3. 3

   Measure the resistance across the sensor pins. A standard magnetic pickup speed sensor should show a specific resistance (often between 150 to 200 ohms depending on the exact transmission model); an open circuit (infinite resistance) or a dead short indicates a failed sensor.

4. 4

   Remove the sensor and check the magnetic tip. Metal shavings or debris from normal transmission wear can accumulate on the magnet, blinding the sensor and causing an implausible AC voltage signal.

5. 5

   Verify that the engine RPM sensor is functioning correctly, as the TCU uses this as the baseline for its plausibility calculation.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and disconnect the battery to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the transmission input shaft speed sensor on the exterior of the transmission housing.

3. 3

   Removal

   Disconnect the electrical harness from the sensor. Remove the retaining bolt holding the sensor in place and carefully pull the sensor straight out of the housing.

4. 4

   Clean and Inspect

   If the sensor is covered in heavy metal debris, clean it and inspect the transmission fluid. (Excessive metal may indicate internal clutch or mechanical failure).

5. 5

   Installation

   Lubricate the O-ring on the new speed sensor with clean transmission fluid. Insert the new sensor into the housing and tighten the retaining bolt to OEM torque specifications.

6. 6

   Reconnection

   Reconnect the electrical harness, ensuring the locking tab clicks into place.

7. 7

   Clear Codes

   Reconnect the battery, turn the key switch on, and use the tractor's diagnostic H-Menu or a service tool to clear the stored 161-11 fault code.

8. 8

   Test Drive

   Start the tractor and perform a test drive to ensure the transmission shifts smoothly and the code does not return.